JPH0413947A - Method and apparatus for measuring particles in fluid - Google Patents

Abstract

PURPOSE:To improve detecting sensitivity and to increase a dynamic range by discriminating by a photomultiplier, using a single photon counting method if the number of photoelectric pulses is a predetermined value or less and processing a signal in an analog manner to obtain a particle size and a particle size distribution if it is the predetermined value or more. CONSTITUTION:A signal from a photomultiplier 7 amplified by a preamplifier 8 is branched, one is signal-processed by a single photon counting method, and the other is added with an amplifier 21 and a peak analyzer 22 to signal- process by an analog method. Whether the particle is fine of a predetermined value or less or not is discriminated according to the signal from the photomultiplier 7. If the number of photoelectric pulses is the predetermined value or less and discriminated to be fine, the counting method is used, while if it is the value or more, the signal is processed in an analog manner to obtain a particle size and a particle size distribution. Thus, scattered lights from the fine and large particles can be analyzed.

Description

Detailed Description of the Invention [Industrial Field of Application J] The present invention is a particle measuring device in a fluid, more specifically, a fluid containing particles flowing in a measurement cell is irradiated with a laser beam, and the scattering from the particles is detected. The present invention relates to a method and apparatus for measuring particles in a fluid, which receives light and determines particle diameter and particle size distribution from the intensity of the scattered light.

[Prior art] Currently, the ultrapure water and chemical solutions used in the semiconductor manufacturing process are 4Mbit and 16Mbit, and as the density of SI becomes higher, high quality water that does not contain impurities is required. ing. Among these, it is particularly important to control fine particles in ultrapure water and chemical solutions, as this greatly affects the yield of LSI.

Up until now, scanning electron microscopes have been used to measure particles in ultrapure water and chemical solutions, but these methods have been costly and lack real-time performance. In order to solve this problem, a particle measurement method using a laser light scattering method is becoming popular. This measurement method is
This is an application of the fact that the intensity of scattered light from fine particles irradiated with laser light depends on the diameter of the fine particles.

The intensity of scattered light from spherical particles in a liquid is theoretically calculated by Mie. 1/l of the wavelength of laser light
The intensity of scattered light from particles smaller than O is 5 to 6 of the particle size.
It is known that it is proportional to the power of Therefore, as the particle size becomes smaller, the intensity of scattered light from the particle becomes weaker, so in order to detect such weak light, S
/N must be used. A single photon counting method is known as an effective means for detecting weak light.

First, a conventional apparatus using the single photon counting method will be explained using FIG. 4. In FIG. 4, laser light emitted from a laser light source 1 is focused by a lens 2 onto a measurement region 4 in a measurement cell 3. In FIG. When particles pass through the measurement area 4, they scatter the laser light. The light scattered by the particles is focused by a lens 5 and imaged onto a slit 6. The scattered light from the particles passing through the slit 6 reaches the photomultiplier tube 7, where it is converted into an electrical signal.
It is output as a photoelectron pulse. The electrical signal amplified by the preamplifier 8 is converted into a digital signal by a pulse height discriminator 9 and a pulse waveform shaping circuit 10, and then converted into a digital signal by a pulse counting circuit 1.
1, the digital signals are counted and stored in the memory circuit 12 in chronological order. Then, the time series data stored in the memory circuit 12 is analyzed by the arithmetic unit 13, the particle diameter is calculated from the scattered light intensity, and the particle number density is calculated.

[Problem to be solved by the invention 1 The single photon counting method can eliminate dark current and fluctuations in the multiplication factor that cause noise in photomultiplier tubes, so compared to ordinary analog methods, the S/ N can be improved by 3 to 5 times. Light intensity can be measured by single photon counting by counting the number of photoelectron pulses per unit time. However, there is a limit to the number of photoelectron pulses that can be counted per unit time. This is caused by the time width of the photoelectron pulse and the frequency characteristics of the electrical system that constitutes the photon counting circuit. When light hits the photocathode of a photomultiplier tube, electrons are ejected from the photocathode due to the photoelectric effect. The electrons ejected from the photocathode are sequentially multiplied inside the photomultiplier tube, and each electron ejected from the photocathode is multiplied by about 10 to the sixth power. As the electrons are multiplied by the photomultiplier tube, variations occur in the distance traveled by the electrons, so the output pulse for each electron ejected from the photocathode has a duration.

This time width is usually 2 for side-on photomultiplier tubes.
It is about ns. Therefore, the number of electrons from the photocathode is 2 n
If the photoelectron pulses are emitted at a time interval shorter than s, the photoelectron pulses output from the photomultiplier tube will overlap, making single photon counting no longer possible. Furthermore, even if electrons eject from the photocathode at a time interval longer than the time width of the photoelectron pulse, the -L limit of the number of counts per unit time is determined by the frequency characteristics of the electrical system that constitutes the single photon counting circuit. It ends up.

In this way, using the single photon counting method can improve the S/N by 3 to 5 times compared to the analog method, making it possible to measure even smaller particles. The dynamic range is limited by the time width of the photoelectron pulse and the frequency characteristics of the elements that make up the photon counting circuit, and in conventional devices, the counting rate is 10 8 counts /
The limit was about seconds, and it was not possible to accurately determine the intensity of strongly scattered light from large particles.

Therefore, the present invention has been made to solve these conventional problems, and is a method for measuring particles in a fluid that can accurately measure the characteristics of particles in a fluid regardless of the size of the particles. The object of the invention is to provide a method and a device thereof.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a fluid containing particles flowing in a measurement cell is irradiated with laser light, and scattered light from the particles is received. In a particle measurement method in a fluid that determines the particle size and particle size distribution from the intensity of scattered light, it is determined whether the particles are microparticles with a size smaller than a predetermined value or not according to a signal from a photomultiplier tube that detects the scattered light from the particles. If the number of photoelectron pulses is less than a predetermined value and it is determined to be a fine particle, single photon counting is used, and if it is determined to be greater than a predetermined value, the signal is processed analogously to determine the particle size and particle size distribution. We adopted a configuration that requires the following.

In addition, in the present invention, a particle measuring device in a fluid that irradiates a fluid containing particles flowing through a measurement cell with a laser beam, receives scattered light from the particles, and calculates the particle size and particle size distribution from the intensity of the scattered light. A photomultiplier tube for detecting scattered light from particles, a means for counting photoelectron pulses according to a signal from the photomultiplier tube, and a means for amplifying the signal from the photomultiplier tube for pulse height analysis. , means for determining whether or not the measured particles are fine particles when the number of photoelectron pulses is equal to or less than a predetermined value; and means for calculating the particle diameter and particle size distribution from the signal from the counting means or the pulse height analysis means; The calculation means counts the photoelectron pulses using a single photon counting method if the number of photoelectron pulses is less than a predetermined value and is determined to be a fine particle, and if the number of photoelectron pulses is determined to be greater than a predetermined value, it counts the photoelectron pulses from the pulse height analysis means. We also adopted a configuration that calculates the particle size and particle size distribution by processing the signal in an analog manner.

[Function] With this configuration, the intensity of weak scattered light from small particles can be analyzed using the single photon counting method, and the intensity of strong scattered light from large particles can be analyzed using the analog method.
Two purposes can be achieved: improved detection sensitivity and expanded dynamic range.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

An embodiment of the invention is illustrated in FIG. In this figure, the same parts as in FIG. 4 are given the same reference numerals, and the explanation thereof will be omitted.

In FIG. 1, the signal from the photomultiplier tube 7 that has been amplified by the preamplifier 8 is divided into two parts, one of which is processed by the conventional single photon counting method, and the other which is processed when the scattered light is strong. An amplifier 21 and a pulse height analyzer 22 are added to enable signal processing using an analog method when single photon counting is not possible. The preamplifier 8 is required to have frequency characteristics corresponding to the time width of the photoelectron pulse (approximately 10 19 seconds), but the amplification 2321 is required to have frequency characteristics corresponding to the time width of the particle passing through the laser beam (approximately 10 −3 seconds). ) may be the frequency characteristic corresponding to The signal processing method using the single photon counting method is the same as the conventional method. A signal having a time width for the particles to pass through the laser beam amplified by the amplifier 21 is sent to the pulse height analyzer 22.
A pulse height analysis of the signal is performed, and a particle size distribution is determined by an arithmetic unit 13.

Further, the arithmetic unit 13 determines whether or not the count value counted by the signal from the pulse counting circuit 11 is less than or equal to a predetermined value, and if it is less than or equal to the predetermined value, the arithmetic unit 13 determines that the measured particles are fine particles. Then, the particle size and particle size distribution are calculated using a single photon counting method, and if the particle size is greater than a predetermined value, the particle size and particle size distribution are calculated using an analog method based on the signal from the pulse height analyzer 22. do.

FIG. 2 shows an example of a circuit diagram for realizing this embodiment.

ICI is a preamplifier 8 for amplifying the signal from the photomultiplier tube 7, and IC2 is a pulse height discriminator for signal processing using the photon counting method. Further, IC3 is an amplifier 21 which amplifies the signal amplified by the ICI again and sends the signal to the pulse height analyzer 22 in FIG. 1 for analog signal processing.

The operation of the device configured in this way will be explained below.

The laser light source 1 emits laser light having a spatial intensity distribution as shown in FIG. 3(A). This laser light irradiates particles flowing through the measurement area 4 of the measurement cell 3. The spatial intensity distribution of this laser light is a Gaussian distribution in the TEM00 mode. When a particle with a certain velocity passes through such a laser beam, the temporal envelope of the intensity of scattered light from the particle reflects the spatial intensity distribution of the laser beam.

FIG. 3(B) shows the temporal change in the output signal from the photomultiplier tube 7 when a minute particle passes through the laser beam. Since the scattered light from minute particles is weak, the photoelectron pulses are discrete and do not overlap. Figure 3 (C)
In this case, the pulse height discriminator 9 converts a signal higher than the level indicated by the broken line in FIG. 3(B) into a digital signal. Dark current components smaller than the level of the broken line are removed, and fluctuations in the multiplication factor of the photomultiplier tube can also be removed by digitalization. The pulses whose heights have been discriminated in this way are counted by the pulse counting circuit 11, and the pulses are counted by the memory circuit 1.
2 stores measurement data in chronological order.

FIG. 3(D) shows the time variation of the output signal from the photomultiplier tube 7 when a large particle passes through the laser beam. When a large particle passes through the laser beam, the scattered light from the particle becomes stronger, resulting in overlapping of photoelectron pulses, especially when the laser beam passes through the center. Since such photoelectron pulses have a large value counted by the pulse counting circuit 11, the arithmetic unit 13 determines whether the pulse counted value by the pulse counting circuit 11 is less than or equal to a predetermined value. When the arithmetic unit 14 determines that the particles to be measured are minute particles and the pulse count value is below a predetermined value, the arithmetic unit 14 uses a single photon counting method based on the data stored in the memory circuit 12. Calculate the particle size and particle size distribution.

On the other hand, when the count value by the pulse counting circuit 11 is greater than the predetermined value, as shown in FIG. 3(D), the measured particles are large, so the analog method is The particle diameter and particle size distribution are determined using a predetermined calculation formula.

In the above-described embodiment, the arithmetic unit determines whether the count value of photoelectron pulses is less than or equal to a predetermined value. good.

[Effects of the Invention] As described above, according to the present invention, it is determined whether a particle is a microparticle of a predetermined value or less according to a signal from a photomultiplier tube that detects scattered light from a particle, and the number of photoelectron pulses is determined. If the particle is determined to be a microparticle below a predetermined value, a single photon counting method is used, and if the particle is determined to be above a predetermined value, the signal is processed in an analog manner to determine the particle size and particle size distribution. Therefore, the intensity of scattered light from small particles can be analyzed using the single photon counting method, and the intensity of strongly scattered light from large particles can be analyzed using analog methods, which serve the two purposes of improving detection sensitivity and expanding the dynamic range. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the device of the present invention, FIG. 2 is a more detailed circuit diagram of the circuit in FIG. 1, and FIG.
1 is a signal waveform diagram illustrating the operation of the apparatus, and FIG. 4 is a block diagram showing the configuration of the conventional apparatus. 3...Measurement cell 4-...Measurement area 7...Photomultiplier tube 11...-Pulse counting circuit 13...Arithmetic device or distributor

Claims (1)

[Claims] 1) Particles in the fluid that irradiates a fluid containing particles flowing in a measurement cell with a laser beam, receives scattered light from the particles, and determines the particle size and particle size distribution from the intensity of the scattered light. In the measurement method, it is determined whether or not a particle is a microparticle with a value below a predetermined value according to a signal from a photomultiplier tube that detects scattered light from the particle. A method for measuring particles in a fluid, which is characterized by using a single photon counting method if the particle size is greater than a predetermined value, and by processing the signal in an analog manner to determine the particle size and particle size distribution. 2) A particle measuring device in a fluid that irradiates a fluid containing particles flowing through a measurement cell with a laser beam, receives scattered light from the particles, and calculates the particle size and particle size distribution from the intensity of the scattered light. a photomultiplier tube for detecting scattered light of the photoelectron pulse; means for counting photoelectron pulses according to a signal from the photomultiplier tube; means for amplifying and analyzing the pulse height of the signal from the photomultiplier tube; means for determining whether or not the measured particles are microparticles when the number is less than a predetermined value; and means for calculating the particle diameter and particle size distribution from the signal from the counting means or the wave height analysis means, the calculating means comprising: If the number of photoelectron pulses is less than a predetermined value and it is determined to be a microparticle, the photoelectron pulses are counted using a single photon counting method, and if the number of photoelectron pulses is determined to be greater than a predetermined value, the signal from the pulse height analysis means is A particle measuring device in a fluid that is characterized by determining particle diameter and particle size distribution through analog processing. 3) The apparatus for measuring particles in a fluid according to claim 2, wherein the determination as to whether the particles are microparticles or not is performed within a calculation means.